Hi Ninja,
Thank you for looking into it, hope everything is well.
I've updated all the software before I upgraded the PHP (see attachment).
I use the same 3rd party extensions as on all my client websites as Akeeba backup and RSFireWall.
I had no isues there with upgrading to a higher PHP, so thats why I thought it had to be the template.
I will disabel the template and see how it goes.